The invention relates to railway tank cars and, more particularly, to a method and apparatus in which one or a series of tank cars containing lading which must be heated to permit load/unload handling is provided with a unique vapor line system used to vent vapors during the heating of the lading commodity and a unique top heater coil system for use in freeing the fittings of the vapor line and other fittings prior to fill/emptying of the tank car.
Often the storage tanks of railway tank cars are used to transport lading which must be heated at the delivery site to liquify the lading into a state which promotes flowability for affective unloading. Typically, this heating of the storage tank commodity is accomplished by the use of a steam heater coil system extending along and about the bottom portion of the storage tank as disclosed, for example, in U.S. Pat. Nos. 3,897,807 and 3,685,458. In some instances, this form of lading can produce noxious gases or vapors within the storage tank as the result of the heating process, which gases present a health and/or safety hazard at the delivery site if they should be expelled from the storage tank during unloading. A notable example in this regard of such lading is molten sulfur.
Molten sulfur is generally considered a difficult to handle commodity in its molten state. It is classified as a combustible, and generally is kept at 300.degree. F. or less for storage and handling. Molten sulfur has a sharp phase change above 317.degree. F. and can carmalize, i.e. become very viscous. It solidifies at 238.degree. F. and, in its solid state, is very difficult to reheat and remelt. At temperatures of 300.degree. F. or higher, sulfur combines readily with hydrogen to form hydrogen sulfide H.sub.2 S, a highly poisonous gas. Sequential reaction of sulfur with moist air forms sulfur oxides, which are gases hazardous to health and which can combine with water vapor to form highly corrosive sulfuric acid H.sub.2 SO.sub.4. During the delivery site heating of a molten sulfur tank car, these noxious gases are typically produced and can present a hazardous condition to operating personnel in the unloading operation if these gases are permitted to be expelled into the atmosphere about the storage tank, either through a gas relief value or the drainage port means associated with the tank car.
It is also known in the art to interconnect a series of railway tank cars through the use of induction and eduction conduits mounted adjacent opposed ends of each tank car for the purpose of sequential, consecutive load/unloading of fluid ladings from a single point at one end of the series of tank cars. This sequential unloading concept facilitates the formation of unit trains and is disclosed, for example, in U.S. Pats. 3,897,807 and 4,002,192. It can occur, however, that these induction and eduction conduits become blocked or obstructed with solidified liquid, such as molten sulfur, as a result of previous use or, more typically, the valve units operable in such conduits become obstructed due to solidified fluid. The presence of such solidified fluid in the valve passages of the tank car induction and eduction conduits requires spot correction in order to permit the unloading or loading sequence to operate, presenting a time consuming problem at the delivery site.
The present invention concerns a method and apparatus for obviating these and other tank car handling problems, thus facilitating the unloading of unit tank trains and safeguarding the working environment from noxious gases at the delivery site.